Direct observation of size-selected Ni nanoclusters soft-landed on a Si(111)-(7×7) surface

Ni atoms (Ni1) and nanoclusters (Ni3,Ni9) were deposited on clean Si(111)-(7×7) surfaces by a soft landing method at room temperature. Observations by X-ray photoelectron spectroscopy have revealed that the sticking probability of Ni1 to the Si substrate is significantly smaller than that of Ni3 or Ni9. It was suggested by direct observations using scanning tunneling microscopy that Ni9 clusters are separately fixed to the position where they landed, while Ni3 clusters diffuse on the surface and aggregate into characteristic nanosized structures.